The most common cause of pacemaker-facilitated tachycardia is pacemaker-mediated tachycardia (PMT), also commonly known as endless loop tachycardia. Continuous retrograde conduction through the AV node during ventricular paced beats results in an ongoing loop of atrial sensed—ventricular paced beats. Pacemaker algorithms for identifying and treating PMT are well recognized and effective. Less common and often unrecognized or misdiagnosed is pacemaker-facilitated tachycardia due to atrial tracking. (Wang P J, Chen H, Okamura H, Al-Ahmad A, Hsia H H: Timing Cycles of Implantable Devices. In Ellenbogen K A, Kay G N, Lau C P, Wilkoff B L, eds: Clinical Cardiac Pacing, Defibrillation, and Resynchronization Therapy. 3rd Edition. Philadelphia: WB Saunders, 2007, pp. 969-1004, hereinafter “Wang”) In this circumstance, sinus or atrial tachycardia triggers ventricularly paced beats when the programmed sensed AV interval (SAV) is less than the intrinsic AV interval. In the absence of identifiable P waves, ECG discrimination between these arrhythmias is often indistinct. Furthermore, current pacemaker algorithms are unable to differentiate between these two tachycardias.
We introduce a new method for identifying each of these particular mechanisms of pacemaker-facilitated tachycardia, which is based on the specific termination response to post-ventricular atrial refractory period extension (PVARP).